Fluid delivery systems can be used to deliver a fluid, such as a pharmacological compound (e.g., a therapeutic agent), from a reservoir to a subject, such as a human. In some embodiments, a fluid delivery system includes a housing containing a deformable membrane and a fluid reservoir. The needle is in fluid communication with the fluid reservoir so that as a force is exerted against the deformable membrane, the fluid can exit the system via the needle. The needle is inserted into a subject (e.g., a human) so that the fluid is injected into the subject as the fluid leaves the system.